“So does the head of the school’s history department have two heads are something? Maybe a ‘split personality’, or perhaps ‘in transition’?’
No, they are two different people.
Susan Petrie is the teacher and Andrew Hoey is the head of the history department.
That brings up the question of why a high school needs various departments with department heads. Seems like a lot of unnecessary administrators, unless a department head also does a full load of classroom teaching.